1. Technical Field of the Invention
The present invention relates to a three-dimensional coordinate measuring machine, and particularly, to a moving mechanism of a three-dimensional coordinate measuring machine.
2. Related Art
A three-dimensional coordinate measuring machine is used to measure coordinates of an outline of an object. In the three-dimensional coordinate measuring machine, moving mechanisms that move in three-axis directions, i.e., an X-axis, a Y-axis, and a Z-axis orthogonal to one another, are sequentially configured on a base and a displacement measuring instrument is provided in a member (third moving part) capable of moving in the three-axis directions in the final stage, and then the coordinates of the surface position of an object are calculated by combining the displacement when a probe of the displacement measuring instrument is caused to come into contact with the outline of the object and the coordinate values in the three-axis directions at that time. The coordinates of the position to which each moving mechanism has moved serve as the base of the coordinates to be measured, and therefore, the coordinates of movement are required to be highly accurate.
The moving mechanism of the three-dimensional coordinate measuring machine etc. is implemented by using a linear guide.
FIG. 1A and FIG. 1B are diagrams illustrating a linear guide: FIG. 1A is a perspective view illustrating an external appearance and FIG. 1B is a section view.
The linear guide has a rail 1 and a moving unit 2 that slides and moves on the rail 1. As illustrated in FIG. 1B, the moving unit 2 is in contact with the rail 1 via bearing balls 3 and at the time of movement, the bearing ball 3 rotates. As illustrated in FIG. 1A, there exist rotation components P, Y, and R in three directions in which the moving unit 2 rotates with respect to the rail 1. P is called pitching, Y, yawing, and R, rolling.
When configuring a moving mechanism, in order to remove the influence of the above-described rotations, a plurality of linear guides is used. For example, two moving units that move on the same rail are attached to the same moving part. Due to this, it is possible to reduce the influence of the pitching P and the yawing Y. In this case, the rail is only one, and therefore, it is comparatively easy to perform attachment.
Further, there is a case where a plurality of rails and a plurality of moving units are used. For example, two rails are arranged in parallel and two moving units that move on each rail are attached to the same moving part. In this case, as described above, two moving units may be attached to each rail. In such a case, four moving units are used. Due to this, it is possible to reduce the influence of rolling R, in addition to that of the pitching P and the yawing Y.
FIG. 2 is a diagram illustrating a configuration example of a moving mechanism of a three-dimensional coordinate measuring machine. This configuration is a cantilever system.
The three-dimensional coordinate measuring machine has a base 11 formed of a stone surface plate of compound artificial marble etc., a Y column 21 provided on one of sides of the base 11, two Y-axis rails 22A and 22B provided in parallel on the Y column 21, a Y moving part 31 that moves on the Y-axis rails 22A and 22B, two X-axis rails 32A and 32B provided in parallel on the Y moving part 31, an X moving part 40 that moves on the X-axis rails 32A and 32B, a Z column 41 fixed to the X moving part 40 and which extends in the vertical direction, two Z-axis rails 42A and 42B provided in parallel on the Z column 41, and a Z moving part 50 that moves on the Z-axis rails 42A and 42B. To the Z moving part 50, a displacement measuring instrument 51 is attached and a measuring probe of the displacement measuring instrument 51 is caused to come into contact with the surface of an object to be measured. In the cantilever system moving mechanism, it is possible to access the top of the base 11 from any direction except from the backside, and therefore, there is an advantage that arrangement of an object to be measured, check of the contact position of the measuring probe, etc., can be performed easily.
Since two moving units are arranged on each rail, groups of four moving units are attached to the Y moving part 31, the X moving part 40, and the Z moving part 50. In the configuration in FIG. 2, the two rails provided in parallel are arranged in proximity to each other on the same surface of the same member, and therefore, it is possible to easily arrange them with a high degree of parallelization.
However, in the cantilever system moving mechanism in FIG. 2, although the Y moving part 31 is supported by the two rails 22A and 22B and the four moving units, the portion close to the end is supported, and therefore, displacement occurs on the other end due to bending. The amount of bending changes in moment as the X moving part 40 moves. In other words, the rigidity of the Y moving part 31 is insufficient.
In order to reduce the influence of bending (rigidity) of the above-described cantilever system moving mechanism, a configuration in which both ends of the Y moving part 31 are supported may be used.
FIG. 3 is a diagram illustrating another configuration example of the moving mechanism of the three-dimensional coordinate measuring machine. In FIG. 3, only the configuration for moving the Y moving part 31 is illustrated and the moving mechanisms of the other axes are not shown. The moving mechanism of the type in FIG. 3 is referred to as an L type.
The L-type moving mechanism of the three-dimensional coordinate measuring machine in FIG. 3 has the same configuration as that in FIG. 2 in that one of end parts of the Y moving part 31 is supported by the two Y-axis rails 22A and 22B provided in parallel on the Y column 21, but different from the configuration in FIG. 2 in that a support member 60 for supporting the end part on the opposite side of the Y moving part 31 is provided and the undersurface of the support member 60 is supported by a sub guide 61 arranged on the base 11. The sub guide 61 is, for example, a linear guide.
In the configuration in FIG. 3, the straightness of the sub guide 61 is required to be kept at a very high degree of accuracy. It is possible to represent an error of the straightness of the sub guide 61 as, for example, a variation in the height of the surface of the base 11. If the height 1 of the surface of the base 11 in the sub guide 61 changes by Δ1, the height of the end part on the opposite side of the Y moving part 31 also changes, but one end of the Y moving part 31 is supported by two linear guides of the Y column 21, and therefore, this is equivalent to being fixed. Because of this, the Y moving part 31 bends (warps) and the height of the end part on the opposite side changes by Δ2, resulting in equilibrium. If such bending occurs in the Y moving part 31, the Z moving part 50 inclines and the position of the measuring probe of the displacement measuring instrument 51 changes by Δ3, and therefore, an error in coordinate measurement occurs.
The bending of the Y moving part 31 changes accompanying the movement in the Y-axis direction and also changes depending on temperature etc. It is possible to correct to a certain degree the error in the contact position of the measuring probe due to bending of the Y moving part 31 by a correction formula calculated based on the measurement results of a reference object, but there is such a problem that it is difficult to accurately correct the influence by the change in the amount of bending.
FIG. 4 is a diagram illustrating a configuration example of the moving mechanism of the three-dimensional coordinate measuring machine. This configuration is a so-called bridge system.
In the bridge system three-dimensional coordinate measuring machine, two Y columns 21A and 21B are provided on the sides in opposition to each other on the base 11 and one Y-axis rail 22A is provided on the Y column 21A and one Y-axis rail 22B on the Y column 21B, respectively. In the case where two moving units are used on each rail, to the Y moving part 31, four moving units that move on the two rails 22A and 22B are attached. Other portions are the same as those in the case of FIG. 2.
In the bridge system three-dimensional coordinate measuring machine in FIG. 4, it is necessary to mount the rails after machining the rail attachment surfaces of the two Y columns 21A and 21B to which one set of rails is attached so that the degree of parallelization and straightness are of very high accuracy, and therefore, there is such a problem that the manufacturing costs will be very high. Further, in the bridge system three-dimensional coordinate measuring machine in FIG. 4, the access onto the base 11 is limited, and therefore, there is such a problem that it becomes difficult to arrange an object to be measured, to check the contact position of the measuring probe, etc.
There is also known a so-called gate type three-dimensional coordinate measuring machine in which the Y moving part 31 is formed into the shape like a gate and the Y-axis rails 22A and 22B are provided on the base, but the same problem as that described above exists because it is necessary to machine the bottom surface of the gate type Y moving part 31 so that the degree of parallelization and straightness are of very high accuracy.